Chapter 5: The human tissues

cell junctions

connections between two cells

tight junction

zipper-like, interlocking linkage between two adjacent cells

what causes tight junctions?

transmembrane cell-adhesion proteins allow for the linkage

desmosome

patch that holds cells together

• hook like, J-shaped proteins arise from cytoskeleton

hemidesmosome

half-desmosome that anchors basal cells of epithelium to an underlying basement membrane

gap junctions

formed by ring-like connexons (communicating)

gland

cell or organ that secretes substances for use elsewhere in the body OR releases them for elimination from the body

secretion

product useful to body

excretion

waste product

exocrine glands

contact with surface of epithelium through DUCTS

endocrine glands

no ducts, hormones secreted directly into blood`

exocrine organs

pancreas, salivary glands, mammary glands

endocrine organs

thyroid, adrenal, and pituitary glands

BOTH endocrine and exocrine organs

liver, gonads, pancreas

unicellular glands

predominantly non-secretory

(can be either endocrine or exocrine)

example of unicellular glands

mucus-secreting goblet cells in trachea

endocrine cells of stomach

duct shapes

simple (unbranched)

compound (branched)

tubular gland shape

narrow secretory portion

acinar gland shape

secretory cells form dilated sac (acinus or alveolus)

tubloacinar (or tubuloalveolar)

both tubular and acinar portions

serous glands

thin, watery secretions

productions of serous glands

perspiration, milk, tears, digestive juices

mucous glands

produce mucin (a glycoprotein) which absorbs water to form mucus

goblet cells

unicellular mucous glands

mixed glands

contains both serous and mucous cell types

• produces a mixture of both secretions

eccrine (merocrine)

secretion by exocytosis

eccrine gland examples

tear glands, pancreas, gastric glands

apocrine secretion

lipid droplet covered by membrane and cytoplasm buds from cell surface

EX: milk fat secretion by mammary gland cells

holocrine secretion

cells accumulate a product until they disintegrate

• secretes mixture of cell fragments and synthesized substances

holocrine examples

oil glands of scalp and skin, glands of eyelids

mucous membrane

lines passages that open to the external environment

EX: digestive tracts

serous membrane

internal membrane, covers organs and lines walls of body cavities

hyperplasia

growth of a tissue through cellular multiplication

hypertrophy

growth through enlargement

EX: growth of muscle after exercise

Metaplasia

change from one type of tissue to another

stem cells

undifferentiated cells that can divide and change into more functionally specific cell types such as blood cells (stem cells → metaplasia)